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29 Cards in this Set
- Front
- Back
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The voltage drop across a cable depends on... |
Its cross sectional area and length |
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What is meant by a standard low voltage? |
A nominal voltage of 230V AC, between phase and neutral Peak is 325VAC |
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What is the maximum resistance that an earth conductor can have? |
.5 ohms |
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What is IP? |
Ingress protection |
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Equation for Voltage drop along a cable? |
Vd= (L X I X Vc)/1000 |
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What are the two types of Batteries? |
Primary - Single use Secondary - Rechargable |
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Why is the MEN system important? |
- It provides a continuous low impedance path for fault currents, so that they operate protective devices |
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Fault path in a men system |
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What are the 3 phase conductor colours? |
L1 - Red/Brown L2 - White L3 - Blue N - Black G - Yellow/Green |
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How do you reverse the direction of a universal motor? |
Switch the polarity of the armature |
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What is meant by the current rating of an HRC fuse? |
The maximum current that the fuse is designed to carry continuously (gG) |
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What does the 6kA mean on a Miniature Circuit Breaker (MCB) |
The max current the MCB can safely open |
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What does C16 mean on a MCB? |
The max current the MCB is designed to carry continuously |
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How does a thermistor protect a motor? |
By detecting a rise in temperature, and opening the control circuit once it reaches a pre-determined temperature |
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What does the fusing factor determine? |
The smallest amount of current required to blow the fuse |
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What does the tripping factor determine? |
The smallest amount of current required to trip the breaker |
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How many watts in 1HP? |
746W |
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What can an EST do? |
- Maintenance - Replacement - Servicing |
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What are some methods of starting a motor? |
- Direct On Line (DOL) - Soft Start (using TRIAC's to control voltage) - Electronic VSD controller - Star to Delta (3-phase only) - Capacitor start |
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Name some motor protection devices |
- Thermistor (temperature) - RCBO (residual current breaker with overload protection) - Thermocouple - Phase reversal protection - Single phasing protection (detects the loss of 1 phase) |
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What is the maximum leakage current for a class 2 appliance? |
1mA |
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What is extra low voltage? |
Less than 50V AC, less than 120V DC with no ripple |
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What is the maximum voltage to earth that can supply a handheld appliance? |
250V |
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When working outdoors, how do you protect yourself from electrocution? |
Use an isolating transformer |
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When is an HRC fuse designed to operate? |
A short circuit |
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When is the coil of a MCB designed to operate? |
Under a short circuit |
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What will happen if you connect an ammeter in parallel? |
The fuse will blow due to a short circuit through the meter |
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Which type of switch has a bi-metal strip? |
A simmer stat |
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What are two disadvantages of the MEN system? |
- Disconnected neutrals are hard to find - Large fault currents if there are poor connections |
